Siheung, Gyeonggi tide times

Predictions: Open-Meteo Marine (MeteoFrance SMOC, 0.08° grid) — heights relative to MSL (not chart datum / LAT). Model-derived.

Model-derived from a global ocean grid. Useful indication; expect about ±45 minutes on average vs. a local harmonic gauge, individual stations vary widely. See /methodology for per-region detail. Not for navigation.

Conditions as of 13:00 local time. Refreshes daily.

Predictions: Open-Meteo Marine (MeteoFrance SMOC, 0.08° grid) — heights relative to MSL (not chart datum / LAT). Model-derived. · Not for navigation.

The angler tradition for major/minor fishing windows: major ≈3-hour windows around moon transit and opposition; minor ≈2-hour windows around moonrise and moonset. Times are Asia/Seoul local. Folk tradition, not a scientific forecast.

Next spring tide on Mon 18 May (range 8.3m). Last neap on Sat 16 May. Next neap on Thu 21 May.

Spring tides cluster around new and full moons (biggest swings). Neap tides land on quarter moons (smallest swings). See the spring tide and neap tide glossary entries for the why.

Siheung (시흥) sits on the eastern shore of Gyeonggi Bay, directly south of Incheon, where the Yellow Sea — Koreans call it the West Sea — delivers some of the largest tidal ranges in Asia. The bay acts as a funnel: the broad Yellow Sea shelf concentrates tidal energy as it narrows toward the coast, producing mean spring ranges of 6.0 to 8.0 m at Siheung. At a high spring tide, the water fills the bay to its brim. Six hours later, at low water, the sea retreats 5 to 8 km from the shoreline, exposing a vast grey-brown plain of tidal flat — the Gyeonggi Bay mudflats — that stretches to the horizon. The scale of that exposure matters practically. At low water on a spring ebb, the tide drops roughly 7 m in six hours, averaging about 1.2 m per hour. The flats drain progressively: first the shallow channels empty, then the upper flat, then the mid-flat, and finally the lower flat, revealing firm sediment that has been building for centuries. Those mudflats are among the most productive coastal ecosystems in East Asia, supporting dense communities of bivalves, polychaete worms, and crustaceans. In spring and autumn, shorebirds gather in the tens of thousands — red-necked stints, dunlins, bar-tailed godwits — feeding on the invertebrates exposed at low water. The feeding windows are strictly tidal: birds arrive within minutes of the flat becoming accessible and depart as the tide returns. Oido (오이도), a low basalt hill 3 km west of central Siheung, was once a proper tidal island, surrounded by sea at high water and connected to the mainland only by a narrow sandspit at the lowest tides. The reclamation that formed the Sihwa Industrial Complex in the 1980s and 1990s changed that permanently. A causeway now runs across what used to be open tidal flat, and Oido is effectively a peninsula. The original village settlement at the island's western tip — a cluster of low buildings dating from the era of tidal isolation — remains visible, and the walkway along the causeway gives a concrete sense of how much flat the sea once covered. At low spring tide, you can see the old channel beds on either side of the causeway, still draining water hours after high water. The Sihwa Lake seawall, completed in 1994, was built to create a freshwater reservoir from a large coastal embayment north of Oido. The plan failed: the enclosed water became severely eutrophied within a few years, and the gates were opened to tidal flushing in 1997 to restore water quality. Today the seawall separates Sihwa Lake from the sea, but tidal exchange flows through large sluice gates. The gates produce strong tidal currents — up to 3 knots through the openings during ebb — that anglers target from the seawall structure. The timing depends on the gate operation schedule, which follows the tidal cycle, not a fixed clock. That same tidal head difference — 5 to 8 m between sea level and Sihwa Lake at ebb — became the basis for the Sihwa Tidal Power Plant, opened in 2011. The plant uses 10 submerged bulb turbines to generate electricity as the sea ebbs through the barrage; incoming flow is managed separately. At 254 MW installed capacity, Sihwa is the world's largest tidal barrage power station by output. The plant generates approximately 550 GWh per year — enough to supply around 500,000 households — using no fuel and producing no direct emissions. The barrage structure is visible from the seawall road; the turbine hall sits below the waterline, so what you see above the surface is primarily the access road and the gate infrastructure. For anglers, Siheung offers productive fishing from the seawall and from the tidal channels on the flat — flatfish (광어, flounder) and sea bass (농어) move onto the flat at high water and concentrate in channels as the tide falls. The productive window is the last two hours of the ebb and the first hour of flood, when fish are channelled into predictable locations. Kayakers and SUP paddlers use the calmer periods around high slack water to explore the margins of Sihwa Lake through the connecting channels, though the strong ebb currents near the sluice gates require respect. Photographers working the mudflats should plan around a morning ebb on a spring tide: the flat is fully exposed by 09:00 on those days, shorebird activity peaks in the first hours of low water, and the light from the east catches the wet sediment surface. Tide data for Siheung, Gyeonggi comes from the Open-Meteo Marine API, a gridded model product. Timing accuracy is ±45 minutes, height accuracy ±0.3 m — usable for trip planning, not for navigation.